Fiber optic cable for inhibiting breaching fluid flow

ABSTRACT

Fiber optic cables suitable for use in downhole applications, with one or more features for inhibiting flow of any fluid breaching an armor layer of the optical cable are provided. By preventing, or at least impeding, fluid flow along the cable length, any breaching fluid may be confined to a small region of the cable, which may significantly reduce the deleterious effects (e.g., hydrogen darkening) of an armor layer breach. One example optical cable generally includes one or more optical fibers, an inner tube surrounding the one or more optical fibers, an outer tube surrounding the inner tube, and one or more polymer sealing features disposed in an annulus between the outer tube and the inner tube and bonded to at least one of the inner tube or the outer tube to prevent fluid flow in the annulus along at least a portion of a length of the optical cable.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/864,205, filed Jan. 8, 2018 and entitled “FIBER OPTIC CABLE FORINHIBITING BREACHING FLUID FLOW,” which is herein incorporated byreference in its entirety.

FIELD OF THE DISCLOSURE

Aspects of the present disclosure generally relate to opticalcommunications and, more particularly, to fiber optic cables for use inharsh environments, such as high pressure, high temperature hydrocarbonrecovery applications.

DESCRIPTION OF THE RELATED ART

With advancements in the area of fiber optic sensors for use in harshenvironments, there is an increasing need for fiber optic cablescompatible with the harsh environmental conditions present in downholeoil and gas applications. For example, fiber optic cables utilized indownhole sensing applications should be able to operate reliably inconditions that may include temperatures in excess of 300° C., staticpressures in excess of 138,000 kilopascal (kPa), vibration, corrosivechemistry, and the presence of high partial pressures of hydrogen.Hydrogen tends to degrade the optical properties of the fibers in anoptical cable, causing undesired attenuation known as hydrogendarkening.

SUMMARY OF THE DISCLOSURE

Certain aspects of the present disclosure provide an optical cablesuitable for downhole use. The optical cable generally includes one ormore optical fibers, an inner tube surrounding the one or more opticalfibers, an outer tube surrounding the inner tube, and one or morepolymer sealing features disposed in an annulus between the outer tubeand the inner tube and bonded to at least one of the inner tube or theouter tube to prevent fluid flow in the annulus along at least a portionof a length of the optical cable.

Certain aspects of the present disclosure provide an optical cablesuitable for downhole use. The optical cable generally includes one ormore optical fibers; an inner tube surrounding the one or more opticalfibers; an outer tube surrounding the inner tube; a filler materialdisposed in at least one of the inner tube or an annulus between theouter tube and the inner tube, along at least a portion of a length ofthe optical cable; and a plurality of feedthroughs configured toencapsulate the filler material in the at least one of the inner tube orthe annulus, wherein the filler material is configured to impede theflow of an ingressing fluid along the at least the portion of the lengthof the optical cable.

Certain aspects of the present disclosure provide an optical cablesuitable for downhole use. The optical cable generally includes one ormore optical fibers, an inner tube surrounding the one or more opticalfibers, and an outer tube surrounding the inner tube and configured toform one or more fluid-tight annular seals with the inner tube toprevent fluid flow in an annulus between the outer tube and the innertube, along at least a portion of a length of the optical cable.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description,briefly summarized above, may be had by reference to various aspects,some of which are illustrated in the appended drawings. It is to benoted, however, that the appended drawings illustrate only typicalaspects of this disclosure and are therefore not to be consideredlimiting of its scope, for the disclosure may admit to other equallyeffective aspects.

FIG. 1 is a transverse cross-sectional view of a conventional fiberoptic cable suitable for use in downhole oil and gas applications.

FIG. 2A is a longitudinal cross-sectional view of an example fiber opticcable suitable for use in downhole oil and gas applications with afluid-tight annular seal, according to certain aspects of the presentdisclosure.

FIG. 2B is a transverse cross-sectional view of the fiber optic cable ofFIG. 2A through line segment AA′.

FIG. 2C is a transverse cross-sectional view of an example fiber opticcable with a fluid-tight annular seal and a buffer layer disposedbetween an outer tube and an inner tube, according to certain aspects ofthe present disclosure.

FIG. 3A is a longitudinal cross-sectional view of an example fiber opticcable suitable for use in downhole oil and gas applications with one ormore polymer sealing features, according to certain aspects of thepresent disclosure.

FIG. 3B is a transverse cross-sectional view of the fiber optic cable ofFIG. 3A through line segment BB′.

FIG. 3C is a transverse cross-sectional view of an example fiber opticcable with a buffer layer disposed between an outer tube and an innertube and a polymer sealing feature disposed between the outer tube andthe buffer layer, according to certain aspects of the presentdisclosure.

FIG. 4A is a longitudinal cross-sectional view of an example fiber opticcable suitable for use in downhole oil and gas applications withfeedthrough-encapsulated filler material, according to certain aspectsof the present disclosure.

FIG. 4B is a transverse cross-sectional view of the fiber optic cable ofFIG. 4A through line segment CC′.

FIG. 5A is a longitudinal cross-sectional view of an example fiber opticcable suitable for use in downhole oil and gas applications with abuffer layer and feedthrough-encapsulated filler material, according tocertain aspects of the present disclosure.

FIG. 5B is a transverse cross-sectional view of the fiber optic cable ofFIG. 5A through line segment DD′.

FIG. 6 is a longitudinal cross-sectional view of an example fiber opticcable suitable for use in downhole oil and gas applications with abuffer layer and feedthrough-encapsulated filler material, according tocertain aspects of the present disclosure.

FIG. 7 is a longitudinal cross-sectional view of an example fiber opticcable suitable for use in downhole oil and gas applications withfeedthrough-encapsulated filler material, according to certain aspectsof the present disclosure.

To facilitate understanding, identical reference numerals have beenused, wherever possible, to designate identical elements that are commonto the figures. It is contemplated that elements disclosed in one aspectmay be beneficially utilized in other aspects without specificrecitation.

DETAILED DESCRIPTION

Certain aspects of the present disclosure provide fiber optic cablessuitable for use in downhole applications, with one or more features forinhibiting flow of any fluid breaching an armor layer of the opticalcable. By preventing, or at least impeding, fluid flow along at least aportion of a length of the optical cable, any breaching fluid may beconfined to a small region of the cable, which may significantly reducethe effects of an armor layer breach. These effects may includecorrosion and the resulting production of hydrogen, which may lead tohydrogen darkening of the optical fibers.

FIG. 1 is a cross-sectional view of a conventional fiber optic cable 100suitable for use in harsh environments, such as downhole oil and gasapplications. The fiber optic cable 100 may be similar to fiber opticcables disclosed in U.S. Pat. No. 7,646,953 to Dowd et al., entitled“Fiber Optic Cable Systems and Methods to Prevent Hydrogen Ingress” andissued Jan. 12, 2010, herein incorporated by reference in its entirety.The fiber optic cable 100 includes a fiber in metal tube (FIMT) core 102surrounded by an outer tube 104. The FIMT core 102 includes an innertube 106 surrounding one or more optical fibers 108. Although threeoptical fibers 108 are shown disposed within the inner tube 106 in FIG.1, the FIMT core 102 may include more or less than three optical fibers.A filler material 114 is disposed in the inner tube 106 andsubstantially fills the void spaces within the inner tube surroundingthe optical fibers 108 to support and prevent the optical fibers 108from moving excessively within the inner tube 106. The filler material114 may also include a hydrogen absorbing/scavenging material tominimize the effects of hydrogen on the optical performance of theoptical fibers 108.

A buffer material 112 is disposed between the outer tube 104 and theinner tube 106. The buffer material 112 provides a mechanical linkbetween the inner tube 106 and the outer tube 104 to prevent the innertube 106 from sliding within the outer tube 104. Additionally, thebuffer material 112 keeps the inner tube 106 generally centered withinthe outer tube 104 and protects the inner tube 106 and any coatingsformed thereon from damage due to vibrating against the outer tube 104.Separation between the buffer material 112 and the outer tube 104creates an outer annular flow path 110, whereas spacing between theinner tube 106 and the buffer material 112 provides an inner annularflow path 116. The buffer material 112 isolates the inner annular flowpath 116 from the outer annular flow path 110, at least until cross-overis desired.

Conventional optical cable designs may be susceptible to leaks in theouter tube (e.g., through pin holes in the weld seam or abrasion of thearmor). Such leaks may allow fluid to enter the optical cable, and thisbreaching fluid may then propagate within the cable. The propagation ofbreaching fluid in the cable may cause various problems, such ascorrosion of inner layers which produces hydrogen (that can lead tohydrogen darkening of optical fibers located therein), bunching offibers which produce bend loss, and attacking any polymer materials inthe cable assemblies. For example, if hydrogen gas is inside the cable,then this can lead to distributed loss in the optical fibers that willnegatively impact the sensing system, particularly for Raman distributedtemperature sensing (DTS).

Attempts have been made to mitigate this problem and reduce ingressroutes in various ways. For example, an (aluminum) buffer layer may beintroduced into fiber optic cables to prevent fluid ingress through thetube walls and hydrogen production. However, cable joints andterminations may still provide a fluid entry point that may be difficultto seal at either end of each cable section. Fluid blockers with fiberfeedthroughs can be introduced at cable joints to prevent movement ofliquids and, to some extent, gases beyond a given cable section, but maybe difficult to make effective against hydrogen, may be time-consumingto install, and may not protect the cable section in which the ingressis actually occurring.

Accordingly, there is a need for a fiber optic cable for use in harshenvironments that is less susceptible to the propagation of breachingfluids. Certain aspects of the present disclosure prevent, or at leastimpede, fluid flow along at least a portion of a length of an opticalcable, thereby confining any fluid breaching the cable to a small regionthereof.

Fiber Optic Cable with Mechanical Seal

Certain aspects of the present disclosure provide a fluid-tightmechanical annular seal between the armor layer (e.g., the outer tube)and the inner tube. If any fluid breaches the armor layer, the breachingfluid will be confined by the gas-tight and liquid-tight seal betweenthe two layers to a small region of the fiber optic cable, unable topropagate up or down the cable, unlike the propagation that can occur inconventional cable designs. Such a tight mechanical seal significantlyreduces the effects of an armor breach in a downhole optical cable.

For certain aspects, the fluid-tight annular seal may be made during thearmoring process, for example, by drawing the armor through a die or byroll-reducing, such that the armor layer has a tightly sealed fit to theinner tube along a desired portion of the cable's length. For otheraspects, the seal may be created in a post-armoring process, forexample, by drawing the armored tube through a die such that the armorlayer (or at least a portion thereof) is reduced to snugly fit a tubeinternal to the cable (e.g., the inner tube) and to produce afluid-tight seal along the length of the cable (or at least a portionthereof). For certain aspects, at any point prior to the formation ofthe seal, the internal tube may be coated with a material (e.g.,fluorinated ethylene propylene (FEP)) to facilitate the forming of aseal with the armor layer.

FIGS. 2A and 2B illustrate an example of a fiber optic cable 200 with afluid-tight annular seal in longitudinal and transverse cross-sections,respectively, according to certain aspects of the present disclosure.The cable 200 comprises a fiber in metal tube (FIMT) core 202 disposedin a protective outer tube 204 (e.g., an armor layer). The FIMT 202comprises an inner tube 206 surrounding one or more optical fibers 208.Although three optical fibers 208 are shown in FIGS. 2A and 2B, thefiber optic cable 200 may include more or less than three opticalfibers. A filler material 210 may be disposed in the inner tube 206 tofill the void spaces not occupied by the optical fibers 208.

For certain aspects, the inner tube 206 and the outer tube 204 maycomprise the same material, such as the same metal or metal alloy. Inother aspects the inner tube 206 and the outer tube 204 may comprisedifferent materials, such as different metals or metal alloys.

The inner tube 206 may be fabricated from a corrosion-resistantmaterial. Examples of suitable corrosion-resistant metal alloys include,but are not limited to, 304 stainless steel, 316 stainless steel,INCONEL® 625, and INCOLOY® 825, among others. Examples of suitableplastics include, but are not limited to fluoropolymers,ethylene-chlorotrifluoroethylene, fluoroethylenepropylene,polyvinylidene fluoride, polyvinylchoride, HALAR®, TEFLON®, and TEFZEL®,among others. The outer diameter of the inner tube 206 may be in therange of about 1.1 to about 4.2 mm, such as about 2.4 mm. Although theinner tube 206 is described as being about 1.1 to about 4.2 mm indiameter, the outer diameter of the inner tube 206 may vary, dependingupon the materials used and the number of optical fibers 208 to beplaced in the inner tube 206.

In one aspect, the inner tube 206 has a wall thickness suitable for aseam-welding process utilized to fabricate the tube from a coil of metalstrip. For example, the wall thickness of a 304 stainless steel innertube may be about 0.2 mm to facilitate a continuous laser weld during atube-forming process. In another aspect, the inner tube 206 has a wallthickness suitable for fabrication by plastic extrusion.

In some sections of the fiber optic cable 200 for certain aspects, theouter tube 204 has an inner diameter D, which is greater than an outerdiameter of the inner tube 206. In these sections, there may be a gap(e.g., an annulus) between the outer tube 204 and the inner tube 206. Inother sections of the fiber optic cable 200, the outer tube 204 has aninner diameter d that is equal to the outer diameter of the inner tube206. In the one or more areas where d is equal to the outer diameter ofthe inner tube 206, the outer tube 204 tightly surrounds the inner tube206, forming one or more fluid-tight annular seals between the outertube 204 and the inner tube 206 to prevent fluid flow (e.g., the flow ofhydrogen gas) therebetween, at least along the portion(s) of the fiberoptic cable 200 with the seal(s).

For certain aspects, the fluid-tight annular seals may be distributedintermittently throughout a length of the optical cable (i.e., the outertube 204 intermittently sealingly contacts the inner tube 206 along thislength). For other aspects, the fluid-tight annular seal may becontinuous, at least along one or more portions of the optical cable(i.e., the outer tube 204 continuously sealingly contacts the inner tube206 along these portions or the entire length of the optical cable). Incertain aspects, both intermittent and continuous fluid-tight annularseals may be employed in different areas of the optical cable.

The fluid-tight annular seal may be made or enhanced by an optionalcoating (not shown) to facilitate the forming of a seal between theinner tube 206 and the outer tube 204. The optional coating may bedisposed on at least one of the inner surface 214 of the outer tube 204or the outer surface 213 of the inner tube 206. The coating may beapplied to the surface(s) 213, 214 at any point prior to the reductionin the diameter of the outer tube 204 to form the mechanical seal. Thecoating may be coated, plated, or otherwise applied in any suitablemanner and may comprise a low hydrogen permeability material, such astin (Sn), aluminum (Al), or other suitable material.

A filler material 210 may be disposed in the inner tube 206 andsubstantially fill the void spaces within the inner tube 206 surroundingthe optical fibers 208 to support and prevent the optical fibers 108from moving excessively within the inner tube 206. The filler material210 has sufficient viscosity to resist the shear forces applied theretoas a result of the weight of the optical fibers 208 when disposed in avertical well installation at elevated temperatures, thereby supportingthe optical fibers 208 without subjecting the fibers to the strain oftheir own weight. The filler material 210 has an operating temperaturerange of about 10 to about 200° C. However, the cable 200 may beutilized over a wider temperature range.

The filler material 210 may also be configured to allow the opticalfibers 208 to relax and straighten with respect to the inner tube 206due to differences in the coefficients of thermal expansion between theoptical fiber 208 and the inner tube 206 and during spooling,deployment, and use of the cable 200. The filler material 210 may alsoprevent chaffing of the coatings on the optical fibers 208 as a resultof bending action during installation and vibration of the cable 200.The filler material 210 may also serve as cushion for the optical fiber208 against the surface of the inner tube 206 to avoid microbend lossesacross cable bends. Suitable filler materials 210 include thixotropicgels or grease compounds, some of which are commonly used in the fiberoptic cable industry for water blocking, filling, and lubrication ofoptical fiber cables. Optionally, the filler material 210 may be omittedfor certain aspects.

The optical fibers 208 are selected to provide reliable transmission ofoptical signals through the cable 200 when disposed in a wellbore, forexample. Suitable optical fibers 208 include low defect, pure silicacore/depressed clad fiber. Alternatively, suitable optical fibers 208include germanium-doped single-mode fiber or other optical fibersuitable for use in a high temperature, high pressure environment. Theoptical fibers 208 disposed within the inner tube 206 may be composed ofthe same type or of different types of materials. The total number offibers 208 and the diameter of the inner tube 206 may be selected toprovide sufficient space to prevent microbending of the optical fibers208 during handling and deployment of the cable 200.

As the fiber optic cable 200 has an operating temperature ranging atleast between about 10° C. to about 200° C. or higher, a greater lengthof optical fibers 208 may be disposed per unit length of inner tube 206to account for the different coefficients of thermal expansion (CTEs)possessed by the optical fibers 208 and the inner tube 206. The innerdiameter of the inner tube 206 is configured to accept an excess lengthof “serpentine over-stuff” of optical fiber 208 within the inner tube206. In one aspect, the excess length of optical fiber 208 may beachieved by inserting the fiber 208 while the inner tube 206 is at anelevated temperature, for example, during laser welding of the innertube 206. The temperature of the inner tube 206 is controlled such thatit approximates the anticipated maximum of normal operating temperaturefor the final installation. In another aspect, the excess length offiber 208 may be achieved by inserting the fiber 208 at a faster ratethan the inner tube 206 is moving on the welding line. This process maylead to an excess length of fiber 208 of up to 2.0% or more within theinner tube 206 after cooling of the inner tube 206, but typically in therange 0.3% to 0.6%.

The outer tube 204 may be manufactured of a corrosion-resistant materialthat easily diffuses hydrogen. The outer tube 204 may be manufactured ofthe same material as the inner tube 206 and may be fabricated with orwithout a coating of a low hydrogen permeability coating orhydrogen-scavenging material. Examples of outer tube materials includesuitable corrosion-resistant metal alloys such as, but not limited to,304 stainless steel, 316 stainless steel, INCONEL® 625, and INCOLOY®825, among others.

In one aspect, the outer tube 204 is seam welded over the FIMT core 202.The weld seam of the outer tube 204 may be fabricated using a tungsteninert gas (TIG) welding process, a laser welding process, or any othersuitable process for joining the outer tube 204 over the FIMT core 202.

Additionally, the outer tube 204 may be rolled or drawn down against theFIMT core 202, where care is taken not to extrude or stretch the FIMTcore 202 such that the excess length of the fibers 208 within the FIMTcore 202 is not appreciably shortened. In aspects where the outer tube204 and the FIMT core 202 are configured to form one or more fluid-tightannular seals with the inner tube to prevent fluid flows, the inner andouter tubes 206, 204 may be fabricated from the same material tominimize differences in thermal expansion.

An initial inner diameter of the outer tube 204 may be selected withsufficient space so as not to damage the FIMT core 202 during welding.The outer tube 204 may be drawn down to a final outer diameter afterwelding. In one aspect, the outer tube 204 has a final outer diameter Dof less than about 3/16 inch to less than about ¼ inch and has a wallthickness in the range of about 0.7 to about 1.2 mm.

For certain aspects, a buffer layer 212 (e.g., analogous to buffermaterial 112) is disposed between the outer tube 204 and the inner tube206 as illustrated in the transverse cross-sectional view of FIG. 2C.The buffer layer 212 provides a mechanical link between the inner tube206 and the outer tube 204 to prevent the inner tube 206 from slidingwithin the outer tube 204. Additionally, the buffer layer 212 keeps theinner tube 206 generally centered within the outer tube 204 and protectsthe inner tube 206 and any coatings formed thereon from damage due tovibrating against the outer tube 204. In this case, the fluid-tightannular seal 205 may be created between the inner surface of the outertube 204 and the outer surface of the buffer layer 212. The fluid-tightannular seal may be created in a similar manner as described above,where the buffer layer 212 surrounding the FIMT core 202 replaces theFIMT core alone in the description of FIGS. 2A and 2B.

For certain aspects, any separation in particular sections of the fiberoptic cable 200 between the buffer layer 212 and the outer tube 204creates an outer annular flow path (e.g., analogous to path 110 in FIG.1), whereas spacing between the inner tube 206 and the buffer layer 212provides an inner annular flow path (e.g., analogous to path 116 in FIG.1). In these sections, the buffer layer 212 isolates the inner annularflow path from the outer annular flow path, at least until cross-over isdesired.

Fiber Optic Cable with Polymer Sealing

Certain aspects of the present disclosure provide a polymer layer bondedbetween the inner tubing and the armor layer (e.g., the outer tube) ofan optical cable to prevent, or at least impede, corrosion and inhibitthe propagation of fluid that may breach the armor layer or other outertube. As used herein and understood by a person having ordinary skill inthe art, the term “fluid” generally refers to a liquid or a gas.Although polymers have been used in optical cables, a polymer has notpreviously been used to form a bond between the armor layer and theinner tube. Expandable foams have been used as insulating and/orcentralizing layers, but such foams do not form a strong bond betweenthe armor layer and the inner tube or a significant protective layer forthe inner tubing.

The polymer layer may coat the inner tube to prevent any ingressingfluids from contacting the inner tube over much of the inner tube'slength, hence inhibiting corrosion of the inner tube and the productionof hydrogen therefrom. The polymer layer may also form a bond betweenthe armor layer and the inner tube such that the polymer materialproduces a pressure barrier that inhibits the propagation of fluids upor down the cable from the point of ingress. Examples of suitablepolymer materials include epoxies and silicone adhesives. To manufacturethe cable, the polymer material may be pumped into an annulus betweenthe armor layer and the inner tube, perhaps using a vacuum pump toevacuate the annulus prior to inserting the polymer material. Thepolymer material may then be cured inside the cable through any ofvarious suitable techniques, such as thermal curing or an additionreaction. The polymer material may form a strong bond to the armorand/or inner tube, not crack under bending or stretching of the cable,be resistant to any chemical attack from ingressing fluid, and retainits physical properties, including at the maximum operating temperaturesof the cable.

FIGS. 3A and 3B illustrate in longitudinal and transversecross-sections, respectively, an example fiber optic cable 300 withpolymer sealing, according to certain aspects of the present disclosure.In the cable 300, one or more optical fibers 308 are surrounded by aninner tube 302 (e.g., in a FIMT core, analogous to FIMT core 202), andthe inner tube 302 is surrounded by an outer tube 304 (e.g., aprotective armor layer, analogous to outer tube 204). The inner diameterof the outer tube 304 is configured to create an annulus 306 between theouter tube 304 and the inner tube 302. One or more polymer sealingfeatures 310 are disposed in the annulus 306.

The one or more polymer sealing features 310 may fill the annulus 306 inone or more sections 311 of the fiber optic cable 300. The one or morepolymer sealing features 310 may be bonded to an outer surface of theinner tube 302, an inner surface of the outer tube 304, or both. Thebonding of the polymer sealing feature 310 to the inner and/or outertube 302, 304 helps to prevent fluid flow (e.g., the flow of hydrogengas) in the annulus 306 along the length of the fiber optic cable 300,thereby confining fluid flow breaching the outer tube 304 to a smallregion between consecutive polymer sealing features 310. The polymersealing features 310 may be mechanically or thermally bonded to theinner and/or outer tubes 302, 304. The polymer sealing features 310 maybe fabricated from, but are not limited to fluoropolymers,ethylene-chlorotrifluoroethylene, fluoroethylenepropylene,polyvinylidene fluoride, polyvinylchoride, HALAR®, TEFLON®, TEFZEL®, andpolytetrafluoroethylene (PTFE), among others. For certain aspects, thepolymer sealing feature(s) 310 may comprise a compressible materialdisposed around the inner tube 302. In this case, the compressiblematerial may be wound around the inner tube 302. In other aspects, thepolymer sealing feature(s) 310 may be composed of a cured material thatis disposed around the inner tube 302.

For certain aspects, the fiber optic cable 300 may also include anothertube 312 disposed between the outer tube 304 and the inner tube 302, asillustrated in the transverse cross-sectional view of FIG. 3C. Forexample, this other tube 312 may be a buffer layer, which may beanalogous to the buffer layer 212 in FIG. 2C. In this case, the polymersealing feature(s) 310 may be disposed in an annulus between the outertube 304 and the other tube 312 (as shown), in an annulus between theother tube 312 and the inner tube 302, or both. The polymer sealingfeature(s) 310 may be bonded to the outer tube 304, to the inner tube302, to an outer surface of the other tube 312, to an inner surface ofthe other tube 312, or any combination thereof. Different axial sectionsof the fiber optic cable 300 may have different arrangements of polymersealing feature(s) 310 with respect to radial location and/or bonding.

Fiber Optic Cable with Feedthrough-Encapsulated Filler Material

Certain aspects of the present disclosure utilize a full or at leastnearly full (close to 100%, such as within 5%) material fill of a tubecontaining the optical fiber(s) (the fiber tube) to prevent the pressurebuildup of fluid in the cable, which might otherwise allow the fluid topush its way along the fiber tube. The filler material may include anyof various suitable materials (e.g., a gel or liquid) capable ofpreventing ingressing fluid from pushing its way up the tubing as thepressure increases. To prevent propagation of the ingressing fluid withbuilt-up pressure, the material fill may be full or close to 100% fullin certain sections. For certain aspects, the filler material may allowthe optical fibers to move sufficiently to allow the fiber overstuff(i.e., the excessive fiber length) to accommodate thermal expansion ofthe cable with increased temperature. For certain aspects, the fillermaterial may be largely incompressible to prevent the fluid pressurebuildup from compressing the filler material down a significantproportion of the cable. For certain aspects, the filler material mayhave adhesive properties that help suppress any pressure buildup. Forfabricating the optical cable, the filler material may initially be alow viscosity fluid that is pumped or otherwise injected into the fibertube and then may be, for example, cured or otherwise processed toachieve its final properties. For certain aspects, it may be possible tocut the fiber tube and remove the exposed section of filler materialfrom the fiber tube to allow splicing or termination of the opticalfibers at cable joints or terminations.

For certain aspects, the resistance of the filler material to thepressure buildup may be aided by fiber feedthroughs that hold back thepressure and/or prevent movement of the filler material. In conventionalcable designs, filler material can be pushed aside by ingressing fluidas the pressure builds up, allowing the ingressing fluid to propagate upand down the cable. Unlike conventional designs, the fiber feedthroughsin certain aspects of the present disclosure need not provide aleak-free seal to fluids, but may be designed simply to preventsignificant leakage of the filler material. The fiber feedthroughs maybe disposed, for example, at the ends of cable sections to provide apressure barrier or at least a backstop to inhibit significant leakageof the filler material from the cable under any internal cable pressurebuildup due to an ingressing fluid. The filler material, either on itsown or in combination with the fiber feedthrough, should prevent, or atleast impede, the progression of the ingressing fluid down the fibertube.

FIGS. 4A and 4B illustrate in longitudinal and transversecross-sections, respectively, an example fiber optic cable 400 withfeedthrough-encapsulated filler material, according to certain aspectsof the present disclosure. In the cable 400, one or more optical fibers408 are surrounded by an inner tube 402 (e.g., in a FIMT core, analogousto FIMT core 202), and the inner tube 402 is surrounded by an outer tube404 (e.g., a protective armor layer, analogous to outer tube 204). Theinner diameter of the outer tube 404 is configured to create an annulus406 between the outer tube 404 and the inner tube 402. A filler material412 may be disposed in the annulus 406 between the inner tube 402 andthe outer tube 404 (as illustrated in FIG. 4A. Additionally oralternatively, filler material may be disposed in the inner tube 402(e.g., analogous to filler material 210 the FIMT core 202 in FIGS. 2Aand 2B). The filler material in the inner tube 402 may be the same or adifferent material from the filler material 412 in the annulus 406.Fiber feedthroughs 410 are configured to encapsulate the filler material412 in the inner tube 402, the annulus 406, or both while stillpermitting the fibers 408 to pass therethrough and extend the length ofthe fiber optic cable 400. The filler material 412 is configured toimpede the flow of an ingressing fluid along at least a portion of thelength of the fiber optic cable 400 that includes the filler material.For certain aspects, the filler material 412 completely fills (or atleast nearly completely fills) the inner tube 402, the annulus 406, orboth. As described above, the filler material 412 may comprise a gel ora liquid, for example.

FIGS. 5A and 5B illustrate in longitudinal and transversecross-sections, respectively, an example fiber optic cable 500 with abuffer layer and feedthrough-encapsulated filler material, according tocertain aspects of the present disclosure. In the fiber optic cable 500,one or more optical fibers 508 are surrounded by an inner tube 502(e.g., in a FIMT core, analogous to FIMT core 202). The inner tube 502is surrounded by a buffer tube 506 (e.g., analogous to the buffer layer212), and the buffer tube 506 is surrounded by an outer tube 504 (e.g.,a protective armor layer, analogous to outer tube 204). With theaddition of the buffer tube 506 an inner annulus 514 is created betweenthe buffer tube 506 and the inner tube 502, and an outer annulus 512 iscreated between the buffer tube 506 and the outer tube 504.

In some aspects, a filler material 510 may be disposed in the outerannulus 512. For certain aspects, a filler material 511 may be disposedin the inner annulus 514. The filler material 510 and/or 511 isconfigured to impede the flow of an ingressing fluid along at least aportion of the length of the fiber optic cable 500. Fiber feedthroughs516 are configured to encapsulate the filler material 510 and/or 511 inat least a portion of either the outer annulus 512 or the inner annulus514, respectively. As illustrated in FIG. 5A, the fiber feedthroughs 516may encapsulate only the filler material 511 in the inner annulus 514.However, as illustrated by the dashed lines 517, the fiber feedthroughs516 for other aspects may have a larger diameter sufficient toencapsulate the filler material 510 and/or 511 in the respective annuli512 and/or 514. The filler material 510 may comprise a gel or a liquid(e.g., a low viscosity liquid). The filler material 510 may be curable.Additionally, the filler material 510 and/or 511 may completely (ornearly completely) fill either or both of the outer annulus 512 or theinner annulus 514, respectively.

To further reduce the effects of hydrogen on the optical fibers 508, thefiller material 510 may optionally include or be impregnated with ahydrogen absorbing/scavenging material, such as palladium or tantalum,and the like. For example, the hydrogen absorbing/scavenging materialmay be a vanadium-titanium wire coated with palladium. Alternatively,the buffer tube 506 and/or the inner tube 502 may be coated with ahydrogen absorbing/scavenging material below an optional coating or onthe interior surface of the buffer tube 506 and/or the inner tube 502,or such a hydrogen absorbing/scavenging material may be impregnated intothe tube material, or any combination of the above.

FIG. 6 is a longitudinal cross-sectional view of an example fiber opticcable 600 suitable for use in downhole oil and gas applications with abuffer tube and feedthrough-encapsulated filler material, according tocertain aspects of the present disclosure. The cable 600 includesmultiple sections (two sections are shown), where adjacent sections maybe joined by a cable splice tube 608 (a cable joint). The cable 600 issomewhat similar in construction to the cable 500 described above,having a FIMT core comprising one or more optical fibers 602 surroundedby an inner tube 610 (e.g., analogous to the inner tube 502) disposedwithin a buffer tube 612 (e.g., analogous to the buffer tube 506). Thebuffer tube 612 is disposed within a protective outer tube 606 (e.g.,analogous to the outer tube 504). A filler material 604 is disposed inthe inner tube 610 and may substantially fill the void spaces within theinner tube surrounding the optical fibers 602 to prevent, or at leastimpede, propagation of an ingressing fluid due to increased pressure.For certain aspects, the filler material 604 may also include a hydrogenabsorbing/scavenging material to minimize the effects of hydrogen on theoptical performance of the optical fibers 602. A pair of fiberfeedthroughs 614 may encapsulate the filler material 604 in the innertube 610 for one or more sections of the fiber optic cable 600. Othersections of the cable 600 may not include fiber feedthroughs, as shown.

FIG. 7 is a longitudinal cross-sectional view of an example fiber opticcable 700 suitable for use in downhole oil and gas applications withfeedthrough-encapsulated filler material, according to certain aspectsof the present disclosure. The cable 700 includes multiple sections (twosections are shown), where adjacent sections may be joined by a cablesplice tube 708 (a cable joint). Each section of the cable 700 mayinclude one or more optical fibers 702 surrounded by a protective tube706, thereby forming a FIMT. A filler material 704 (e.g., somewhatanalogous to the filler material 412) is disposed in the tube 706 andmay substantially fill the void spaces within the tube surrounding theoptical fibers 702 to not only support and prevent the optical fibers702 from moving excessively within the tube 706, but also to prevent, orat least impede, propagation of an ingressing fluid with built-uppressure. For certain aspects, the filler material 704 may also includea hydrogen absorbing/scavenging material to minimize the effects ofhydrogen on the optical performance of the optical fibers 702. A pair offiber feedthroughs 710 may encapsulate the filler material 704 in thetube 706 for one or more sections of the fiber optic cable 700. Othersections of the cable 700 may not include fiber feedthroughs, as shown.

While the foregoing is directed to aspects of the present disclosure,other and further aspects of the present disclosure may be devisedwithout departing from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. An optical cable suitable for downhole use, comprising: one or moreoptical fibers; an inner tube surrounding the one or more opticalfibers; an outer tube surrounding the inner tube; a filler materialdisposed in at least one of the inner tube or an annulus between theouter tube and the inner tube, along at least a portion of a length ofthe optical cable; and a plurality of fiber feedthroughs configured topermit the one or more optical fibers to pass therethrough and toencapsulate the filler material in the at least one of the inner tube orthe annulus, wherein the filler material is configured to impede a flowof an ingressing fluid along the at least the portion of the length ofthe optical cable.
 2. The optical cable of claim 1, wherein the fillermaterial completely fills the at least one of the inner tube or theannulus, along the at least the portion of the length of the opticalcable.
 3. The optical cable of claim 1, wherein the filler materialcomprises a gel or a liquid.
 4. The optical cable of claim 1, whereinthe filler material is curable.
 5. The optical cable of claim 1, whereinthe filler material comprises a low viscosity fluid.
 6. The opticalcable of claim 1, further comprising a buffer layer disposed between theouter tube and the inner tube, wherein the filler material is disposedin at least one of a first annulus between the outer tube and the bufferlayer or a second annulus between the buffer layer and the inner tube,along the at least the portion of the length of the optical cable. 7.The optical cable of claim 1, wherein the ingressing fluid compriseshydrogen gas.
 8. An optical cable suitable for downhole use, comprising:one or more optical fibers; an inner tube surrounding the one or moreoptical fibers; and an outer tube surrounding the inner tube andconfigured to form one or more fluid-tight annular seals with the innertube to prevent fluid flow in an annulus between the outer tube and theinner tube, along at least a portion of a length of the optical cable.9. The optical cable of claim 8, wherein at least a portion of an outersurface of the inner tube is coated with a coating to help form the oneor more fluid-tight annular seals.
 10. The optical cable of claim 9,wherein the coating comprises fluorinated ethylene propylene (FEP). 11.The optical cable of claim 8, wherein the outer tube and the inner tubecomprise the same material.
 12. The optical cable of claim 11, whereinthe outer tube and the inner tube comprise the same metal or metalalloy.
 13. The optical cable of claim 8, wherein the outer tubeintermittently sealingly contacts the inner tube along the at least theportion of the length of the optical cable.
 14. The optical cable ofclaim 8, wherein the outer tube continuously sealingly contacts theinner tube along the at least the portion of the length of the opticalcable.
 15. The optical cable of claim 8, further comprising another tubesurrounding the one or more optical fibers, wherein the inner tubesurrounds the other tube and wherein the inner tube comprises a bufferlayer between the outer tube and the other tube.